MSc

Investigations were carried out in the Department of pomology and Floriculture, Vellanikkra, Thrissur 680654, Kerala, during the period from April 1990 to March 1991 to find out the varietal differences of polyembryonic rootstocks with respect to percentage of success, survival and growth parameters of softwood grafts of mango. Also anatomical studies of graft union were done to find out the different stages of healing process and the possible reasons for graft failure.

Five polyembryonic varieties of mango (Puliyan, Chandrakaran, Olour, Tolikaipan and Muvandan) and one monoembrynoic variety (Bangalora) were selected as rootstocks. Scions of two varieties, Viz. Neelum and Banganapally were used for softwood grafting. One month old rootstocks were grafted in June, July and August.

The results of the study showed that the germination percentage of all polyembryonic varieties are comparatively higher than Bangalora, the monoembryonic variety. Tolikaipan gave the maximum germination percentage. It was observed that percentage of polyembryony ranged from 9.76 to 49.54 for the polyembryonic varieties, the lowest for chandrakaran and highest for Muvndan variety.
The observation on the effect of rootstock, scion and month of grafting on sprouting and survival of graft revealed that puliyan rootstock was most ideal with regard to sprouting and survival. Success percentage was higher for Muvandan - Neelum and Muvandan-Banganapally combinations followed by Puliyan - Neelum and Puliyan Banganapally combinations. However, Puliyan rootstocks grafted with Neelum and banganapally scions gave higher survival percentage. Poor success rate was noted for chandrakaran - Banganapally and Bangalora-Neelum combinations. Survival of grafts was least for Tolikaipan rootstock grafted with Neelum or Banganapally scions. As to the combined effect, Muvandan and Chandarakaran rootstocks grafted with Neelum during June resulted in better initial success. Whereas, survival was higher for Puliyan Banganapally August combination.

With regard to growth parmeters studied, girth of stock, girth of scion and length of sprout are much influenced by rootstock, scion, month of grafting and their interactions. Bangalora, the monoembryonic rootstock, produced the thickest stock and scion throughout the period of study. Among the polyembryonic varieties, Muvandan produced thicker stock and scion. 01 our and chandarakaran rootstocks produced lesser girth of stock and girth of scion respectively. Longer sprouts were also produced by Bangalora. Sprout length was minimum for 01 our. Among the scions, Neelum was found to be superior producing thicker stock, scion and longer sprouts. Similarly, grafting in July was found to be better with respect to these growth parameters. The monoembryonic rootstock, Bangalora, grafted with Neelum either in July or August recorded higher girth of stock, scion and sprout length. Polyembryonic rootstocks grafted with banganapally, generally, found to be less vigorous with respect to these parameters.

Anatomical studies revealed four different stages of graft union i.e. callus initiation stage, callus tissue formation and cambial cell developmental stage, cambial bridge formation stage and a healed union stage. Graft take was faster in Bangalora and Puliyan varieties where as it was slower in Chandrakaran and 01 our varieties. Graft failure was mainly due to failure in callus initiation, formation of necrotic layer and improper alignment of stock and scion.